Start/stop vehicles may be frequently automatically stopped by a controller in response to operating conditions to conserve fuel. For example, an engine of a stop/start vehicle may be stopped in response to a vehicle stop after the engine has reached a predetermined temperature. However, if there is an absence or a low level of vacuum for vehicle brakes or other systems, the automatic stop may be delayed until a desired level of vacuum is achieved. Consequently, less fuel may be saved since the vehicle continues to operate until a desired level of vacuum is provided.
Stop/start vehicles may also have unique circumstances related to engine cooling and frequent engine stops and starts. In particular, if an engine is at operating temperature and is then stopped, engine temperature may increase since coolant may not be pumped from the engine to the cooling system without engine rotation. Further, if the engine is started and stopped at frequent intervals, more engine heat may be retained instead of being rejected to a radiator or heater core since the engine may have less opportunity to pump coolant from the engine.
Thus, automatic engine starting and stopping can increase fuel economy when operating conditions permit engine stopping; however, operation of vehicle accessories (e.g., vacuum pumps, coolant pumps, and alternators) may limit opportunities to stop the engine since stopping the engine may interfere with operation of the accessories.
The inventors herein have recognized the above-mentioned disadvantages and have developed an engine accessory drive system, comprising: an engine; a vacuum pump; a coolant pump configured to supply liquid coolant to the engine; and an electrically driven motor coupled to the vacuum pump and the coolant pump.
By coupling a vacuum pump and a coolant pump to an electrically driven motor it may be possible to increase vehicle fuel economy since the engine may not be required to continue operating for the sole purpose of producing vacuum or reducing engine heat. In addition, since it may be desirable to selectively operate a vacuum pump and coolant pump in the absence of engine rotation, system cost and complexity can be reduced by coupling a single electric motor to the vacuum pump and the coolant pump.
In addition, accessory pumps (e.g., engine coolant pump, fuel pumps, transmission pumps, vacuum pumps, and air conditioning pumps) account for a high percentage of parasitic engine load. The inventors herein have recognized that the parasitic losses of these pumps can be reduced by operating the pumps on an as needed basis and by operating the pumps at efficient operating conditions.
The present description may provide several advantages. In particular, the approach can increase vehicle fuel economy since the engine can be stopped without affecting the production of vacuum or coolant flow. In addition, the approach can reduce system cost since a vacuum pump and coolant pump can be driven by a single electric motor rather than by two separate motors. Further, the speed of the motor may be adjusted to account for different priorities between the coolant pump and the vacuum pump.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.